This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-226498, filed Aug. 10, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a load/unload type magnetic disk drive which is constructed in a manner that when a rotation of a magnetic disk is stopped, a magnetic head is mounted on a ramp so as to be unloaded, and when the magnetic disk is rotated, the magnetic head is moved onto the magnetic disk so as to be loaded. In particular, the present invention relates to a magnetic disk drive which can preferably control a movement of carriage for carrying a magnetic head, and to a method of controlling a movement of carriage in an unload operation of a magnetic head.
Conventionally, in general, a contact start and stop method, what we call, a CSS method has been applied to an apparatus which records information in a magnetic disk by a magnetic head, and reproduces the information therefrom, for example, a small-size magnetic disk drive. The above CSS method has the following features.
First, in a CSS type disk drive, in a drive non-operation state, that is, in a state that a magnetic disk functioning as a recording media is not rotated, a magnetic head contacts with the disk. When the magnetic disk is started to rotate, the head receives an air bearing action by an air flow generated between the magnetic disk and the head, so that the head can be floated from the magnetic disk. In the disk drive having the structure as described above, in the initial stage of a rotation start of the magnetic disk and in the final stage of a rotation stop thereof, the head is slid on the magnetic disk in a state of contacting with the magnetic disk. For this reason, there is a possibility that a damage is given to a data area on the magnetic disk. In particular, in the case where an impact or the like is given to the drive from the outside, there is a high possibility that a damage is given to the magnetic disk.
For this reason, in the above CSS type magnetic disk drive, for the duration when the magnetic disk is in a rotation stop state, the head is positioned to a place different from a data zone on the magnetic disk, for example, a ring-like retracting zone for only head, which is secured on an inner peripheral side of the data zone, what we call, a CSS area. In the case where an electric power is supplied to the drive, or in the case where the host system gives an instruction to rotate a spindle motor (i.e., SPM) rotating the magnetic disk at a high speed, the spindle motor rises up by a steady-state speed in a state that the head is positioned to the above CSS area, and thereafter, the head is floated from the magnetic disk. The head is moved to the data zone on the magnetic disk for the first time after being floated. On the other hand, when the host system gives an instruction to stop the spindle motor in a state that the head is positioned to the data zone, the head is retracted to the CSS area, and thereafter, the spindle motor is stopped.
In the case where the head is retracted to the CSS area, by a driving force of a voice coil motor (i.e., VCM), a carriage functioning as a head moving mechanism, that is, an actuator collides with an inner peripheral stopper, and thereby, it is possible to prevent the head from going out of the CSS area.
In recent years, in the light of the concept of improving an impact resistance performance of disk drive and improving a recording density, in place of the aforesaid CSS technique, a head load/unload operation has been proposed such that the head and the magnetic disk have no contact with each other in the case where the magnetic disk is in a rotation stop state. In this load/unload operation, when a rotation of the magnetic disk is stopped, a tab, which is a distal end portion of suspension of the carriage, is slid along a ramp having an inclination provided outside the magnetic disk, and thereby, the head is lifted up from the magnetic disk, then, is retracted outside the disk so as to be unloaded, and thereafter the rotation of the magnetic disk is stopped. Moreover, when a rotation of the magnetic disk is started, that is, in a rotation start state, the rotation of the disk reaches a steady-state speed, and thereafter, the head is moved from the ramp onto the magnetic disk, and thus, is loaded.
In the above load/unload operation, a surface of the magnetic disk, that is, a flatness is improved, and a floating amount of the head is reduced, and thereby, it is possible to improve a recording density of the magnetic disk. In general, in the CSS action, the more the surface, that is, a flatness of the magnetic disk is improved, the head and the magnetic disk contact with each other when the spindle motor is stopped; as a result, the head and the magnetic disk contact with each other, and are mutually attracted. For this reason, there is a problem that it is difficult to apply the above CSS method to a magnetic disk having a high surface accuracy. In order to solve the above problem, it is indispensable to apply a head load/unload operation such that in an operation of the case where the spindle motor is stopped, the head is retracted to the ramp provided outside the magnetic disk so that the head and the magnetic disk becomes a non-contact state.
In such a head load/unload operation, during a head unload operation, the head must be moved at a low speed and at a constant speed so that the head does not contact with the magnetic disk. Usually, in a head load/unload control in the case where a power source is in an on-state, a back (counter) electromotive voltage generated in a voice coil motor is detected, and then, a detection signal is processed by a microprocessor (CPU), and thus, a moving rate or speed xcfx89 of the carriage is controlled to a low desired speed. Conventionally, there is a feedback control system having an unload speed control system block as shown in FIG. 1, as a control system for controlling a moving rate or speed xcfx89 of the carriage to a desired speed xcfx89r.
As well known, in a feedback control system, a follow-up lag is generated. In the head unload operation, the follow-up lag is also generated, and there is a problem that the lag causes the following undesirable results.
First, so long as the head is moved on the magnetic disk to an outer circumferential direction (ramp direction), no external force such as a frictional force or the like acts onto the tab of the distal end of the suspension supporting the head; therefore, an external force acting onto the carriage is small. To the contrary, in a state that the head or the tab is moved on the ramp, a friction is generated between the tab and the ramp, and a load fluctuation (change) acts onto the carriage as a disturbance. In particular, in a head structure using a currently popular negative pressure head as the head, when the head is lifted out of the magnetic disk to the ramp, an external force is required for release a negative pressure generated between the head and the magnetic disk, and this is a load of hindering an unload operation.
As described above, in the above head load/unload type magnetic disk drive, in the head unload operation, when the head is separated from the magnetic disk, an external force of a direction hindering an unload operation rapidly acts onto the carriage. For this reason, there is the following problem in the speed feedback control system as shown in FIG. 1 applied to the conventional magnetic disk drive according to a speed feedback control which is carried out in the following manner that a back electromotive voltage generated in the voice coil motor is measured, and a moving rate or speed xcfx89 of the head or the carriage is detected, and thus, the moving rate or speed xcfx89 is approximated to a desired speed xcfx89r. More specifically, in the above speed feedback control system, a follow-up lag is generated; as a result, a moving rate or speed of the head or the carriage lowers. Moreover, in the above speed feedback control system, in the worst case, when the head starts to be place onto the ramp, that is, when the head collides with the ramp, a phenomenon occurs such that a movement of the head, that is, the carriage is temporarily stopped.
Considering the above phenomenon in the unload operation from the point of view of head floating, the head is positioned on the magnetic disk in a state that a load applied to the head is eliminated. For this reason, in this state, namely, when the head ascends the ramp, a state that a movement of the head is temporarily stopped is continued for a relatively long period, for example, a period more than one rotation of the spindle motor so that due to a run out of the magnetic disk, negative and positive pressures produced between the head and the magnetic disk is unbalanced so that an unstable state takes place in a floating operation. In the aforesaid unstable state, the head and the magnetic disk contact with each other; for this reason, there is a problem that a damage is given to the magnetic disk.
It is, therefore, an object of the present invention to provide a magnetic disk drive which can realize a stably head unload operation, and to provide a control method which can control a stable movement of carriage in an head unload operation.
More particularly, an object of the present invention is to provide a magnetic disk drive which can prevent a great reduction of a carriage moving speed in a ramp collision and a temporary stop of a carriage moving operation and can realize a stable head unload operation by making a detection that the head collides with a ramp when the head is unloaded, and changing a speed feedback gain into a larger value so as to improve a follow-up ability of a feedback control system when detecting a ramp collision, or by applying a feedforward driving force to a voice coil motor, and to provide a method of controlling a movement of the carriage in an head unload operation.
To achieve the above object, the present invention provides a head load/unload type magnetic disk drive including: speed detecting means for detecting a moving speed (VCM speed) of a carriage by observing a back electromotive voltage induced in a coil of a voice coil motor (VCM); and speed control means for controlling an unload speed by carrying out a feedback control on the basis of the carriage moving speed detected by the speed detecting means in a had unload operation of unloading the head to a ramp arranged outside a magnetic disk, wherein the magnetic disk drive is further provided with ramp collision discriminating means which discriminates a ramp collision when the head collides with the ramp on the basis of at least one of the speed detection result by the speed detecting means and a controlled manipulated variable fed back to a VCM side from the speed control means in the head unload operation, and a gain changeover means which changes a speed feedback gain by the speed control means into a high gain side in accordance with a ramp collision discrimination by the ramp collision discriminating means.
In the present invention, the following matter has attracted interest; more specifically, the carriage moving speed detected from the back electromotive voltage generated in the VCM or a controlled manipulated variable fed back to the VCM side from speed control means, reflects a ramp collision as shown in FIG. 5 or 6. The discrimination of the ramp collision is carried out by monitoring at least one of the above carriage moving speed and the controlled manipulated variable to the VCM, and then, in the case where the ramp collision is detected, the speed feedback gain is changed into a high gain side.
As described above, according to the present invention, the ramp collision is detected, and at this time, the speed feedback gain is changed into a high gain side so as to improve a follow-up ability of the speed feedback control system. By doing so, it is possible to prevent a great reduction of a carriage moving speed in a ramp collision and a generation of a temporary stop of the carriage moving operation, and to realize a stable head unload operation.
The above ramp collision discrimination may be made on the basis of either the above carriage moving speed (detected from the back electromotive voltage generated in the VCM) or the above controlled manipulated variable (fed back to the VCM side from the speed control means). Further, the ramp collision discrimination is made on the basis of the former and the latter, and thereby, it is possible to obtain a high accurate discrimination. In this case, the above ramp collision discriminating means may be composed of: first discriminating means which makes a first ramp collision discrimination on the basis of the carriage moving speed; second discriminating means which makes a second ramp collision discrimination on the basis of the controlled manipulated variable; and third discriminating means which finally makes a ramp collision on the basis of these two ramp collision discriminations. Preferably, either of the following discriminating logics may be applied to the above third discriminating means; more specifically, the discriminating logics include: a first discriminating logic of discriminating a ramp collision in the case where the above two ramp collision discriminating results both show a ramp collision; and a second discriminating logic of discriminating a ramp collision in the case where at least one discriminating result shows a ramp collision.
According to the above first discriminating logic, it is possible to prevent a disadvantage such that a ramp collision discrimination is made in error due to an influence such as a noise in the case where no ramp collision takes place, and thus, to carry out a ramp collision discrimination with a high accuracy. Moreover, according to the above second discriminating logic, it is possible to prevent a disadvantage such that no ramp collision discrimination is made in error regardless of the case where a ramp collision takes place, and thus, to carry out a ramp collision discrimination with a high accuracy. In addition, a decision which the first or second discriminating logic should be applied, may be made by making much of which the ramp collision is discriminated in error or the ramp collision is not discriminated in error.
In the case where a ramp collision is discriminated before a timer counts a predetermined time from the unload operation start, and the predetermined time elapses, by canceling the discrimination, it is possible to prevent a disadvantage such that a ramp collision discrimination is made in error regardless of the case where no ramp collision takes place.
In addition, the above ramp collision discrimination may be made on the basis of a magnitude of an external force acting on the carriage or a change of the external force. The external force acting on the carriage can be calculated on the basis of the above carriage moving speed and the above controlled manipulated variable.
In place of the above gain changeover means, feedforward compensating means may be provided so as to add a predetermined feedforward manipulated variable to the controlled manipulated variable fed back to the VCM side in accordance with the ramp collision discrimination by the ramp collision discriminating means.
As described above, when a ramp collision is detected, the predetermined feedforward manipulated variable added to the controlled manipulated variable from the speed control means is given to the VCM side, and thereby, it is possible to prevent a great reduction of a carriage moving speed in a ramp collision and a temporary stop of a carriage moving operation, and to realize a stable head unload operation.
In a manufacturing stage of the magnetic disk drive, a feedforward manipulated variable peculiar to the disk drive is calculated, and information indicative of a driving force of the disk drive is previously stored in memory means. Then, when a ramp collision is detected, by reading out the information indicative of the feedforward manipulated variable stored in the memory means, it is possible to generate the corresponding feedforward manipulated variable and to give it to the VCM. In particular, an operation for re-calculating the feedforward manipulated variable is carried out in accordance with a using condition of the magnetic disk drive, for example, for each rise of the disk drive, and thereby, it is possible to acquire an optimal feedforward manipulated variable always suitable for the disk drive.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.